(a) Field of the Invention
The present invention relates to a motor control system and method for an environmentally-friendly vehicle, and more particularly, to a motor control system and method for an environmentally-friendly vehicle that reduces torque ripples due to characteristics of a motor system while the environmentally-friendly vehicle is running at ultra-low speed in an electric vehicle (EV) running mode.
(b) Description of the Related Art
As is well known in the art, environmentally-friendly vehicles, which include a fuel cell vehicle, an electric vehicle, a plug-in electric vehicle, and a hybrid vehicle, typically include one or more motors and engines to generate driving power. The environmentally-friendly vehicles generally include a motor system 10 that has an inverter and a motor device, as shown in FIG. 1.
The inverter of the motor system 10, as a power converter which converts direct current (DC) voltage input from a DC terminal into alternating current (AC) voltage based on a driving condition, may include a control/gate board configured to process input/output signals and a power module formed of power conversion switching devices. The motor device of the motor system 10 is an apparatus that converts electrical energy into mechanical energy to drive the environmentally-friendly vehicle.
Furthermore, the motor system 10 is operated by a motor control system, as shown in FIG. 2. The motor control system as shown in FIG. 2 may include a 2-dimensional current command generator, a current controller, a coordinate transformer, a PWM (pulse width modulation) inverter, to operate the motor. The motor control system may sequentially perform operations as follows.
1. The 2-dimensional current command generator of the motor control system may generate a d-axis and q-axis (d/q axis) current command (idq*) using a torque command (T*), a motor speed (ω), and a reference voltage (Vdc) to be input.
2. The current controller may be configured to generate a d-axis and q-axis (d/q axis) voltage command (vdq*), and the coordinate transformer may transform the d/q axis voltage command (vdq*) into a 3-phase voltage command (Vabc*).
3. The PWM signal generator may convert the 3-phase voltage command into a switching signal (Sabc).
4. When the switching signal is input to the PWM inverter, the PWM inverter may produce 3-phase current (iabc) to drive the motor.
However, even though the motor control system may typically operate the motor system of the environmentally-friendly vehicle, when the environmentally-friendly vehicle runs at ultra-low speed in an EV (electric vehicle) mode, surge vibrations may occur, thus drivability may deteriorate. Particularly, when the environmentally-friendly vehicle is driven on a sloped road at ultra-low speed and with high torque, the surge vibrations may occur more than on a level road.
When the surge vibrations occur, since drivability and merchantable quality may decrease, measures to reduce surge vibrations are required. Surge vibrations may occur in the environmentally-friendly vehicle when a frequency of torque ripples based on characteristics of the motor system is resonant with a natural frequency of a driving-transmission apparatus (e.g., a reducer), and conventional methods to compensate for the surge vibrations are as follows.
A method in the prior art reduces torque ripples of the motor system by an optimal design of a motor shape. In particular, the method in the prior art reduces torque ripples by an optimal design for slot and teeth shapes of a motor stator, and by an optimal disposal design for permanent magnets of a rotor of the motor. However, since the method in the prior art needs to have a prototype to perform a verification test, and to repeat related processes when the verification test is unsatisfactory, a considerable amount of time and cost for development are required.
The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.